Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 273

Caution The card's writing/reading speeds required for recording movies (card performance requirements) vary depending on the movie recording quality. Before recording movies, see Cards that can record movies to check card performance requirements. Movie Recording Size Image size Image Size 5472×2886 4096×2160 * 4096×2160 3840×2160 1920×1080 Aspect Ratio 17:9 17:9 17:9 16:9 16:9 * Movies can be cropped around the center of the image, as if recorded with a telephoto lens. Caution If you change the [ : Video system] setting, also set [ : Movie rec quality] again. Other devices may not play movies such as 4K, / , and High Frame Rate movies normally, because playback is processing-intensive. Apparent resolution and noise vary slightly depending on movie recording quality and settings for the lens used. Note To obtain better performance with the card, formatting the card with the camera before recording movies is recommended ( ). Movies cannot be recorded in HD or VGA quality. 273